ABSTRACT. The effects of intravenous infusion of hypotonic lactated Ringer's (LR: n=14) on plasma volume and venous blood gases were compared to those of hypotonic Ringer's solutions (RS: n=7) in diarrheic Japanese Black breed calves with metabolic acidosis. V enous blood samples were collected immediately before and after, and at 24 hr after the fluid infusion therapy. The LR and RS infusions increased relative plasma volume to 147.1 ± 25.5% and 134.2 ± 18.6%, respectively, just after the fluid therapy. The LR infusion induced an increase in the BE value (+5.1 ± 4.8 mM) at 24 hr compared to that of RS. LR infusion should be explored as a treatment for dehydration and moderate metabolic acidemia caused by naturally occurring diarrhea in calves.